Inconsistent types for variable with partial type

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Assessment

Difficulty
4/5
Estimated time
3-5 days
Newbie friendliness
45/100
Issue type
Bug
Clarity
Mostly clear
Activity status
Stale
Tech stack
python
Domain
devtools

Research direction

Start by reproducing the Python snippet with mypy, including both regular and fine-grained incremental mode, and inspect the revealed types and reachability results. Done means x is consistently inferred as int, every line is considered reachable, and both modes agree.

Written by the indexing model from the issue text.

Description

bug topic-fine-grained-incremental

In the example below the variable seemingly has two types (None and x) which is wrong. This also results in an inconsistency with fine-grained incremental mode.

x = None

def f() -> None:
    reveal_type(x)  # None
    if x:
        1()  # No error, considered as not reachable
        y = 1
    else:
        y = ''  # No error

x = 1
reveal_type(x)  # int

The expected behavior is for x to always have the type int and for every line in the example to be considered reachable.

Dominant language
Python
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Merged PRs (30d)
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